Vision (1) Flashcards
What is the output cell of the retina?
Retinal ganglion cells
Which brain structures do RGCs run to?
Lateral geniculate nucleus - in thalamus
Superior colliculus
Suprachiasmatic nucleus
Where do neurons from the LGN project to?
V1
Where do neurons from the superior colliculus project to?
Pulvinar nucleus - in thalamus
Then to specialised regions of visual cortex - beyond V1
What is the purpose of saccades?
Focus most important part of scene on fovea
What is within the inner segment of a photoreceptor?
Cell body
What is within the outer segment of a photoreceptor?
Stacks of membranous discs - for phototransduction
What are the 3 types of cones and which colours do they detect?
Short - blue light
Medium - green light
Long - red light
Which photoreceptor cell type is found in the fovea?
Cones
What is the resting membrane potential of photoreceptors and why?
-40mV (depolarised) - due to Na+ and Ca2+ influx
What happens to the membrane potential of photoreceptors when excited?
Hyperpolarisation
What is the off response of a photoreceptor?
In dark - depolarised - continuously releasing glutamate
What is the on response of a photoreceptor?
In light - hyperpolarised - reduced glutamate release
What are the type of bipolar cells and their responses?
On cells - inhibitory receptors - depolarise when glutamate not released - excited by photoreceptor hyperpolarisation
Off cells - excitatory receptors - hyperpolarise when glutamate not released - inhibited by photoreceptor hyperpolarisation
What is the role of horizontal cells and how do they work?
Lateral inhibition - increase resolution of stimulus localisation
Release GABA onto photoreceptors - prevents glutamate release
What image properties do RGCs encode?
Form
Colour
Motion
What are the 3 types of RGCs?
Midget
Parasol
Koniocellular
What is the most common type of RGC?
Midget
What do midget RGCs detect?
Static images - details and colours
What do parasol RGCs detect?
Motion and change
What is the key difference in firing between midget and parasol RGCs?
Midget - sustained firing in response to sustained stimulus
Parasol - firing only in response to stimulus change
